The present invention relates to an electrical switchgear and, more particularly, to a wheel/rail structure of a drawout circuit breaker truck assembly for restraining the circuit breaker truck assembly under fault conditions in a frame of the switchgear.
With reference to FIG. 1, a conventional switchgear, generally indicated at 10, includes a circuit breaker truck assembly, generally indicated at 11. The truck assembly 11 includes a circuit breaker truck 12 that carries racked-in power circuit breaker 13 so that the circuit breaker 13 can be withdrawn from a frame 14 of the switchgear 10 for maintenance. In particular, the frame 14 includes at least one rail 15. Wheels 16 (only one shown in FIG. 1) are mounted to at least one side of the circuit breaker truck 12. The wheels 16 are supported by the rail 15 such that an inside portion of each wheel 16 of the circuit breaker truck 12 slides on the rail 15. Under short circuit conditions, there are moments on the circuit breaker poles that cause the circuit breaker truck assembly 11 to twist about its horizontal and vertical axes. This movement may force the circuit breaker truck assembly 11 to jump off the rails 15 and raises the possibility of an arc initiation if the primary contacts separate from the bushings.
Thus, there is a need to provide an improved rail and breaker wheel arrangement so as to restrain the circuit breaker truck assembly in place under fault conditions.